Thank you @OzarkEdge - the RSSI setting to -55 has solved the problem - all works again as expected.Could be the 86U 2.4 radio failing. There are reviews online to this affect.
You could make the 86U a remote node to see if the issue moves with it. And then move it back with a clean install.
One more idea... try lowering your Roaming Assistant 2.4 RSSI to -55. Maybe your layout puts your 2.4 client in node contention since 2.4 travels far. I have a suspcion that the new SDK in .386 firmware has boosted the 2.4 signal effectiveness.